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Without this patch, the setting SSH.StartBuiltinServer decides whether the native (Go) implementation is used rather than calling 'ssh-keygen'. It's possible for 'using ssh-keygen' and 'using the built-in server' to be independent. In fact, the gitea rootless container doesn't ship ssh-keygen and can be configured to use the host's SSH server - which will cause the public key parsing mechanism to break. This commit changes the decision to be based on SSH.KeygenPath instead. Any existing configurations with a custom KeygenPath set will continue to function. The new default value of '' selects the native version. The downside of this approach is that anyone who has relying on plain 'ssh-keygen' to have special properties will now be using the native version instead. I assume the exec-variant is only there because /x/crypto/ssh didn't support ssh-ed25519 until 2016. I don't see any other reason for using it so it might be an acceptable risk. Fixes #23363 EDIT: this message was garbled when I tried to get the commit description back in.. Trying to reconstruct it: ## ⚠️ BREAKING ⚠️ Users who don't have SSH.KeygenPath explicitly set and rely on the ssh-keygen binary need to set SSH.KeygenPath to 'ssh-keygen' in order to be able to continue using it for public key parsing. There was something else but I can't remember at the moment. EDIT2: It was about `make test` and `make lint`. Can't get them to run. To reproduce the issue, I installed `golang` in `docker.io/node:16` and got: ``` ... go: mvdan.cc/xurls/v2@v2.4.0: unknown revision mvdan.cc/xurls/v2.4.0 go: gotest.tools/v3@v3.4.0: unknown revision gotest.tools/v3.4.0 ... go: gotest.tools/v3@v3.0.3: unknown revision gotest.tools/v3.0.3 ... go: error loading module requirements ``` Signed-off-by: Leon M. Busch-George <leon@georgemail.eu>
313 lines
9.3 KiB
Go
313 lines
9.3 KiB
Go
// Copyright 2021 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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package asymkey
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import (
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"crypto/rsa"
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"crypto/x509"
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"encoding/asn1"
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"encoding/base64"
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"encoding/binary"
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"encoding/pem"
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"fmt"
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"math/big"
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"os"
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"strconv"
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"strings"
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"code.gitea.io/gitea/modules/log"
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"code.gitea.io/gitea/modules/process"
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"code.gitea.io/gitea/modules/setting"
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"code.gitea.io/gitea/modules/util"
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"golang.org/x/crypto/ssh"
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)
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// ____ __. __________
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// | |/ _|____ ___.__. \______ \_____ _______ ______ ___________
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// | <_/ __ < | | | ___/\__ \\_ __ \/ ___// __ \_ __ \
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// | | \ ___/\___ | | | / __ \| | \/\___ \\ ___/| | \/
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// |____|__ \___ > ____| |____| (____ /__| /____ >\___ >__|
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// \/ \/\/ \/ \/ \/
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//
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// This file contains functions for parsing ssh-keys
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//
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// TODO: Consider if these functions belong in models - no other models function call them or are called by them
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// They may belong in a service or a module
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const ssh2keyStart = "---- BEGIN SSH2 PUBLIC KEY ----"
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func extractTypeFromBase64Key(key string) (string, error) {
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b, err := base64.StdEncoding.DecodeString(key)
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if err != nil || len(b) < 4 {
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return "", fmt.Errorf("invalid key format: %w", err)
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}
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keyLength := int(binary.BigEndian.Uint32(b))
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if len(b) < 4+keyLength {
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return "", fmt.Errorf("invalid key format: not enough length %d", keyLength)
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}
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return string(b[4 : 4+keyLength]), nil
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}
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// parseKeyString parses any key string in OpenSSH or SSH2 format to clean OpenSSH string (RFC4253).
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func parseKeyString(content string) (string, error) {
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// remove whitespace at start and end
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content = strings.TrimSpace(content)
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var keyType, keyContent, keyComment string
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if strings.HasPrefix(content, ssh2keyStart) {
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// Parse SSH2 file format.
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// Transform all legal line endings to a single "\n".
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content = strings.NewReplacer("\r\n", "\n", "\r", "\n").Replace(content)
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lines := strings.Split(content, "\n")
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continuationLine := false
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for _, line := range lines {
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// Skip lines that:
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// 1) are a continuation of the previous line,
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// 2) contain ":" as that are comment lines
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// 3) contain "-" as that are begin and end tags
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if continuationLine || strings.ContainsAny(line, ":-") {
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continuationLine = strings.HasSuffix(line, "\\")
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} else {
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keyContent += line
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}
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}
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t, err := extractTypeFromBase64Key(keyContent)
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if err != nil {
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return "", fmt.Errorf("extractTypeFromBase64Key: %w", err)
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}
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keyType = t
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} else {
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if strings.Contains(content, "-----BEGIN") {
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// Convert PEM Keys to OpenSSH format
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// Transform all legal line endings to a single "\n".
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content = strings.NewReplacer("\r\n", "\n", "\r", "\n").Replace(content)
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block, _ := pem.Decode([]byte(content))
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if block == nil {
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return "", fmt.Errorf("failed to parse PEM block containing the public key")
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}
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if strings.Contains(block.Type, "PRIVATE") {
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return "", ErrKeyIsPrivate
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}
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pub, err := x509.ParsePKIXPublicKey(block.Bytes)
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if err != nil {
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var pk rsa.PublicKey
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_, err2 := asn1.Unmarshal(block.Bytes, &pk)
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if err2 != nil {
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return "", fmt.Errorf("failed to parse DER encoded public key as either PKIX or PEM RSA Key: %v %w", err, err2)
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}
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pub = &pk
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}
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sshKey, err := ssh.NewPublicKey(pub)
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if err != nil {
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return "", fmt.Errorf("unable to convert to ssh public key: %w", err)
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}
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content = string(ssh.MarshalAuthorizedKey(sshKey))
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}
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// Parse OpenSSH format.
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// Remove all newlines
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content = strings.NewReplacer("\r\n", "", "\n", "").Replace(content)
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parts := strings.SplitN(content, " ", 3)
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switch len(parts) {
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case 0:
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return "", util.NewInvalidArgumentErrorf("empty key")
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case 1:
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keyContent = parts[0]
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case 2:
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keyType = parts[0]
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keyContent = parts[1]
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default:
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keyType = parts[0]
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keyContent = parts[1]
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keyComment = parts[2]
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}
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// If keyType is not given, extract it from content. If given, validate it.
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t, err := extractTypeFromBase64Key(keyContent)
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if err != nil {
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return "", fmt.Errorf("extractTypeFromBase64Key: %w", err)
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}
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if len(keyType) == 0 {
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keyType = t
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} else if keyType != t {
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return "", fmt.Errorf("key type and content does not match: %s - %s", keyType, t)
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}
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}
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// Finally we need to check whether we can actually read the proposed key:
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_, _, _, _, err := ssh.ParseAuthorizedKey([]byte(keyType + " " + keyContent + " " + keyComment))
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if err != nil {
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return "", fmt.Errorf("invalid ssh public key: %w", err)
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}
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return keyType + " " + keyContent + " " + keyComment, nil
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}
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// CheckPublicKeyString checks if the given public key string is recognized by SSH.
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// It returns the actual public key line on success.
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func CheckPublicKeyString(content string) (_ string, err error) {
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content, err = parseKeyString(content)
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if err != nil {
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return "", err
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}
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content = strings.TrimRight(content, "\n\r")
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if strings.ContainsAny(content, "\n\r") {
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return "", util.NewInvalidArgumentErrorf("only a single line with a single key please")
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}
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// remove any unnecessary whitespace now
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content = strings.TrimSpace(content)
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if !setting.SSH.MinimumKeySizeCheck {
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return content, nil
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}
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var (
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fnName string
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keyType string
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length int
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)
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if len(setting.SSH.KeygenPath) == 0 {
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fnName = "SSHNativeParsePublicKey"
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keyType, length, err = SSHNativeParsePublicKey(content)
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} else {
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fnName = "SSHKeyGenParsePublicKey"
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keyType, length, err = SSHKeyGenParsePublicKey(content)
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}
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if err != nil {
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return "", fmt.Errorf("%s: %w", fnName, err)
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}
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log.Trace("Key info [native: %v]: %s-%d", setting.SSH.StartBuiltinServer, keyType, length)
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if minLen, found := setting.SSH.MinimumKeySizes[keyType]; found && length >= minLen {
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return content, nil
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} else if found && length < minLen {
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return "", fmt.Errorf("key length is not enough: got %d, needs %d", length, minLen)
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}
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return "", fmt.Errorf("key type is not allowed: %s", keyType)
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}
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// SSHNativeParsePublicKey extracts the key type and length using the golang SSH library.
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func SSHNativeParsePublicKey(keyLine string) (string, int, error) {
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fields := strings.Fields(keyLine)
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if len(fields) < 2 {
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return "", 0, fmt.Errorf("not enough fields in public key line: %s", keyLine)
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}
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raw, err := base64.StdEncoding.DecodeString(fields[1])
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if err != nil {
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return "", 0, err
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}
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pkey, err := ssh.ParsePublicKey(raw)
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if err != nil {
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if strings.Contains(err.Error(), "ssh: unknown key algorithm") {
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return "", 0, ErrKeyUnableVerify{err.Error()}
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}
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return "", 0, fmt.Errorf("ParsePublicKey: %w", err)
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}
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// The ssh library can parse the key, so next we find out what key exactly we have.
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switch pkey.Type() {
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case ssh.KeyAlgoDSA:
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rawPub := struct {
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Name string
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P, Q, G, Y *big.Int
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}{}
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if err := ssh.Unmarshal(pkey.Marshal(), &rawPub); err != nil {
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return "", 0, err
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}
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// as per https://bugzilla.mindrot.org/show_bug.cgi?id=1647 we should never
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// see dsa keys != 1024 bit, but as it seems to work, we will not check here
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return "dsa", rawPub.P.BitLen(), nil // use P as per crypto/dsa/dsa.go (is L)
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case ssh.KeyAlgoRSA:
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rawPub := struct {
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Name string
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E *big.Int
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N *big.Int
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}{}
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if err := ssh.Unmarshal(pkey.Marshal(), &rawPub); err != nil {
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return "", 0, err
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}
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return "rsa", rawPub.N.BitLen(), nil // use N as per crypto/rsa/rsa.go (is bits)
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case ssh.KeyAlgoECDSA256:
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return "ecdsa", 256, nil
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case ssh.KeyAlgoECDSA384:
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return "ecdsa", 384, nil
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case ssh.KeyAlgoECDSA521:
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return "ecdsa", 521, nil
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case ssh.KeyAlgoED25519:
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return "ed25519", 256, nil
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case ssh.KeyAlgoSKECDSA256:
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return "ecdsa-sk", 256, nil
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case ssh.KeyAlgoSKED25519:
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return "ed25519-sk", 256, nil
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}
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return "", 0, fmt.Errorf("unsupported key length detection for type: %s", pkey.Type())
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}
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// writeTmpKeyFile writes key content to a temporary file
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// and returns the name of that file, along with any possible errors.
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func writeTmpKeyFile(content string) (string, error) {
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tmpFile, err := os.CreateTemp(setting.SSH.KeyTestPath, "gitea_keytest")
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if err != nil {
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return "", fmt.Errorf("TempFile: %w", err)
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}
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defer tmpFile.Close()
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if _, err = tmpFile.WriteString(content); err != nil {
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return "", fmt.Errorf("WriteString: %w", err)
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}
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return tmpFile.Name(), nil
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}
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// SSHKeyGenParsePublicKey extracts key type and length using ssh-keygen.
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func SSHKeyGenParsePublicKey(key string) (string, int, error) {
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tmpName, err := writeTmpKeyFile(key)
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if err != nil {
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return "", 0, fmt.Errorf("writeTmpKeyFile: %w", err)
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}
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defer func() {
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if err := util.Remove(tmpName); err != nil {
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log.Warn("Unable to remove temporary key file: %s: Error: %v", tmpName, err)
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}
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}()
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keygenPath := setting.SSH.KeygenPath
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if len(keygenPath) == 0 {
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keygenPath = "ssh-keygen"
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}
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stdout, stderr, err := process.GetManager().Exec("SSHKeyGenParsePublicKey", keygenPath, "-lf", tmpName)
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if err != nil {
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return "", 0, fmt.Errorf("fail to parse public key: %s - %s", err, stderr)
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}
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if strings.Contains(stdout, "is not a public key file") {
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return "", 0, ErrKeyUnableVerify{stdout}
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}
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fields := strings.Split(stdout, " ")
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if len(fields) < 4 {
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return "", 0, fmt.Errorf("invalid public key line: %s", stdout)
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}
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keyType := strings.Trim(fields[len(fields)-1], "()\r\n")
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length, err := strconv.ParseInt(fields[0], 10, 32)
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if err != nil {
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return "", 0, err
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}
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return strings.ToLower(keyType), int(length), nil
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}
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